This invention relates to processes for the production of polyol fatty acid polyesters, which processes eliminate the need to synthesize and purify lower alkyl ester intermediates. More particularly, this invention relates to processes for synthesizing polyol fatty acid higher polyesters by reaction of unesterified polyol, preferably selected from the group consisting of monosaccharides, disaccharides, polysaccharides, sugar alcohols, sugar ethers, polyglycerols and polyalkoxylated glycerols, and a second polyol esterified with fatty acids and selected from monoglycerides, diglycerides and triglycerides.
The food industry has recently focused attention on polyol polyesters for use as low-calorie fats in food products. Triglycerides (triacylglycerols) constitute about 90% of the total fat consumed in the average diet. One method by which the caloric value of edible fat can be lowered is to decrease the amount of triglycerides that is consumed, since the usual edible triglyceride fats are almost completely absorbed in the human system (see Lipids, 2, H. J. Deuel, Interscience Publishers, Inc., New York, 1955, page 215). Low calorie fats which can replace triglycerides are described in Mattson, et al., U.S. Pat. No. 3,600,186. Mattson, et al. disclose low calorie, fat-containing food compositions in which at least a portion of the triglyceride content is replaced with a polyol fatty acid ester having at least four fatty acid ester groups, with each fatty acid having from eight to twenty-two carbon atoms.
Rizzi and Taylor, U.S. Pat. No. 3,963,699, describe a solvent-free transesterification process in which a mixture of a polyol (such as sucrose), a fatty acid lower alkyl ester (such as a fatty acid methyl ester), an alkali metal fatty acid soap, and a basic catalyst is heated to form a homogenous melt, to which is added excess fatty acid lower alkyl ester to form the higher polyol fatty acid polyesters. The polyesters are then separated from the reaction mixture. This process for making sucrose polyesters involves two discrete synthesis steps: (1) reaction of triglyceride and lower alkyl alcohol to form lower alkyl esters with glycerine (glycerol) as a by-product, and (2) reaction of sucrose and lower alkyl esters to form sucrose polyesters with a lower alkyl alcohol as a by-product.
Unfortunately, the need to synthesize fatty acid lower alkyl ester intermediates increases the operating costs of the polyol polyester synthetic process, and the reaction of polyol and fatty acid lower alkyl ester results in the production of lower alkyl alcohol as a by-product. Systems for the capture of lower alkyl alcohol are required, and the need to separate and handle the lower alkyl alcohol increases the risk of discharges of alcohol into the environment. Consequently, there exists a need to develop a transesterification process which does not employ fatty acid lower alkyl ester intermediates.
Feuge et al., U.S. Pat. No. 3,714,144, and Feuge et al., J. Amer. Oil. Chem. Soc., 1970, 47(2), 56-60, disclose a solvent-free transesterification process which comprises mixing molten sucrose with esters of fatty acids and alkali-free sodium or potassium soaps under a partial vacuum. The teachings of Feuge et al. are primarily directed to the formation of lower esters; the only specific teaching by Feuge et al. of a method in which the percentage of sucrose esters having three or more fatty acid chains is greater than 35% of the total sucrose esters formed uses methyl carbitol palmitate as a fatty acid source. Unfortunately, methyl carbitol is relatively toxic and would be unsuitable for use in food grade polyol polyester production. The Feuge et al. article further teaches that triglycerides perform poorly as intermediates.
Osipow et al., U.S. Pat. No. 4,380,616, disclose the preparation of sucrose mono- and di-esters by forming a transparent emulsion containing immiscible reactants and maintaining the transparent emulsions under appropriate conditions to permit reaction. Sucrose mono- and di-esters are formed using emulsions containing methyl fatty acid ester and sucrose. Osipow et al. also disclose the formation of mono- and di-glycerides using emulsions containing glycerine and methyl fatty acid esters or glycerol tri-esters.
Parker et al., U.S. Pat. No. 3,996,206, teach that sucrose mono-and di-esters are valuable surfactants, while the sucrose octa-esters are unsatisfactory surfactants. Parker, et al., disclose a process for preparing lower sucrose polyester surfactants by reacting solid particulate sucrose with triglyceride in the presence of a basic transesterification catalyst; the triglyceride and sucrose are used in substantially equimolar amounts.
Gallymore et al., U.S. Pat. No. 4,298,730, disclose a process for preparing a surfactant mixture containing sucrose mono- and di-esters by reacting solid particulate sucrose with a fatty acid triglyceride, a di- and/or mono-glyceride, and a basic transesterification catalyst in the presence of a fatty acid soap. Gallymore et al. teach that sucrose octa-esters are unsatisfactory surfactants, and octa-esters are therefore not prepared in the process.
Cooper et al., U.S. Pat. No. 5,304,665, disclose a method of obtaining highly esterified alkoxylated polyols from triglycerides by contacting an epoxide, an aliphatic polyalcohol, and a triglyceride in the presence of a basic catalyst to accomplish ring-opening of the epoxide and formation of a partially esterified alkoxylated polyol, followed by contacting the partially esterified alkoxylated polyol with fatty acids.
Thus, many prior art methods which react triglycerides and polyol are limited to the synthesis of lower esters, and higher polyesters of polyhydroxy compounds, such as sucrose, are not or cannot be obtained. Additionally, many prior art two-step methods require a basic transesterification catalyst to be used in both steps. The use of such catalysts in both steps increases yield loss and increases color formation in the product. Other prior art methods require the addition of fatty acids in the second step.
Accordingly, it is an object of this invention to obviate various problems of the prior art.
It is another object of this invention to provide novel batch and continuous processes for the production of polyol polyesters, in particular polyol polyesters wherein at least 50%, preferably at least about 70%, more preferably at least about 75%, and even more preferably at least about 95%, of the polyol""s hydroxyls are esterified. Preferred sucrose polyester products are sucrose higher polyesters in which an average of at least 4, and preferably an average of from about 5 to about 8, hydroxyls per polyol molecule are esterified.
It is also an object of this invention to provide novel processes for the production of polyol fatty acid polyesters, which processes eliminate the need to synthesize and purify fatty acid lower alkyl ester intermediates. The processes may be batch or continuous processes.
It is an additional object of this invention to provide novel processes for the production of polyol fatty acid polyesters which eliminate the need to ship, handle, capture, and/or recycle lower alkyl alcohol.
It is also an object of this invention to provide novel processes for the production of polyol fatty acid polyesters which eliminate discharge of lower alkyl alcohol to the environment.
It is yet another object of this invention to provide such processes which provide higher yields and which reduce undesirable color formation.
In accordance with one aspect of the present invention, there is provided both batch and continuous processes for synthesizing polyol fatty acid polyesters comprising the steps of (1) mixing ingredients comprising (a) unesterified first polyol having hydroxyl groups, (b) second polyol esterified with fatty acids, (c) basic catalyst, and (d) emulsifying agent selected from the group consisting of solvents, soaps, and partially esterified polyols, to form a mixture of ingredients; (2) reacting the mixture of ingredients at a temperature sufficient to obtain a reaction mixture of ingredients, reaction products and by-products; (3) removing at least a portion of the by-products from the reaction mixtures; and (4) further reacting the reaction products and ingredients from step (3) at a temperature and for a time sufficient to esterify at least 50%, preferably at least about 70%, more preferably at least about 75%, and most preferably at least about 95%, of the hydroxyl groups of the first polyol. The reaction can be continuous or batch. The basic catalyst, solvent and/or soap can be removed at the completion of the second step.
In accordance with another aspect of the present invention, there is provided processes for synthesizing polyol fatty acid polyesters comprising the steps of (1) mixing ingredients comprising (a) unesterified first polyol, preferably selected from a group consisting of monosaccharides, disaccharides, polysaccharides, sugar alcohols, sugar ethers, polyglycerols, and polyalkoxylated glycerols (b) second polyol esterified with fatty acid chains, (c) basic catalyst and (d) solvent to form a mixture of ingredients; (2) reacting the mixture of ingredients at a temperature sufficient to obtain a reaction mixture of ingredients, reaction products and by-products; and (3) removing at least a portion of the by-products from the reaction mixture; and (4) further reacting the reaction products and ingredients from step (3) at a temperature and for a time sufficient to esterify at least about 50%, preferably at least about 70%, more preferably at least about 75%, and most preferably at least about 95%, of the hydroxyl groups of the first polyol.
In accordance with another aspect of the present invention, there is provided processes for synthesizing sucrose higher polyesters (sucrose polyesters having more than four fatty acids) comprising the steps of (1) mixing ingredients comprising sucrose, fatty acid triglyceride, basic catalyst, and sucrose lower polyesters to form a mixture of ingredients; (2) reacting the mixture of ingredients at a temperature sufficient to obtain a reaction mixture of ingredients, reaction products and by-products; and (3) removing at least a portion of the by-products comprising glycerine, and mono- and di-glycerides from the reaction mixture; and (4) further reacting the reaction products and ingredients from step (3) at a temperature and for a time sufficient to complete the reaction, wherein the molar ratio of the fatty acids of the triglyceride to the hydroxyl groups of the sucrose is not less than 1:1. Preferably at least about 70%, by weight, of the sucrose higher polyesters are sucrose octa-esters.
It has now been found that higher sucrose polyesters can be produced without the use of lower alkyl ester intermediates or methyl carbitol by transesterification of sucrose by triglyceride. Glycerine, mono- and/or di-glycerides, the by-products of the reaction, are derived from the triglyceride when at least one ester group of the triglyceride has been transferred to sucrose. Removal of glycerine, mono- and/or di-glycerides drives the reaction to high degrees of esterification, and polyol penta- to octa-esters are formed. The need to produce fatty acid lower alkyl esters in a separate step and the need to separate lower alkyl alcohol are eliminated by these processes, resulting in more economic processes. Eliminating the production of lower alkyl alcohol also eliminates the risk of the alcohol being released into the environment
It has also surprisingly been found that sucrose polyesters can be produced in a three-step process without using basic transesterification catalysts in the second step. Eliminating the basic transesterification catalyst from the second step provides higher yields and reduces undesirable color formation. A decrease in color formation increases the ease of product purification.
These and additional objects and advantages will be more fully apparent in view of the following detailed description.